Here's how 7 US cities are commemorating 9/11, 25 years later

Today is the 25th anniversary of September 11, 2001, when terrorists hijacked four commercial passenger planes, crashing two into New York's Twin Towers and killing 2,977 people.

Since the attacks, the US has created over 1,100 memorials across all 50 states where visitors can reflect and honor those who died.

Communities have also developed traditions and ceremonies to mark the anniversary. Visitor numbers can vary depending on how the community is connected to the attacks.

New York City's skyline fundamentally changed following the attacks. Twenty-three New York Police Department members died in the line of duty, and hundreds of NYPD officers have died as a result of 9/11-related illnesses.

The ceremony holds seven moments of silence to mark the times when each of the World Trade Center towers was struck, when each tower fell, the Pentagon attack, the United Airlines Flight 93 crash, and those lost to 9/11 health effects.

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Among the various memorials located throughout the city, the New York City Fire Department holds an annual "Walk of Remembrance" earlier in September to honor Father Mychal Judge, a FDNY Chaplain who was killed while ministering to firefighters during the attacks.

The Pentagon's memorial site was designated on Wednesday as an affiliated area of the National Park System. The Pentagon has historically displayed an American flag from the building's roof near the impact zone.

President Donald Trump attended the annual 9/11 ceremony at the Pentagon and delivered remarks. Vice President JD Vance attended the New York City ceremony alongside the four living former presidents, Bill Clinton, George W. Bush, Barack Obama, and Joe Biden.

At the site where United Airlines Flight 93 crashed, located in a small Pennsylvania borough, a two-hour morning observance takes place at the memorial's Wall of Names, from 8:30 a.m. to 10:30 a.m.

Every year, thousands of people take part in a 9/11 Memorial Stair Climb, one of many throughout the nation that honors New York City Fire Department firefighters by climbing or walking the equivalent of the World Trade Center's 110 stories.

The Denver Gazette reported the climb raised about $110,000 for two charities last year, including the FDNY Counseling Services Unit and the National Fallen Firefighters Foundation. About $1.4 million was raised nationwide for first responders and their families.